C＃递归查询

Question

我正在处理一个项目，我使用C＃来填充来自多个源的URL的单个MSSQL表。

该表包含链接重定向信息（下面的示例结构）。

RequestedURL, RedirectedURL 
www.123.com, www.123.com/123 
www.123.com/123, www.123.com/1234/link.asp 
www.123.com/1234/link.asp, www.123.com/12345/link.asp 

我很新的C＃和需要编写某种递归查询都要经过各redirectedurl，如果是在requestedurl然后找到关联redirectedurl。某些网址可能会有多个重定向。

Answer 1

您可以创建一个字典，其中RequestedUrl作为键和RedirectedUrl作为值。所以一旦你找到requestedUrl，你可以找到它的redirectedURL，如果这个redirectedURL有一个redirectedURL，你也可以找到它。

Answer 2

由于您在SQL Server数据库中有此数据，因此可能的方法是CTE的递归。起初，This explanation看起来有点混乱，但我认为如果你向下滚动到这个例子，它将清楚如何做到这一点。

这里没有重复完整的解释，这是这样的查询的例子：

USE AdventureWorks2008R2; 
GO 
WITH DirectReports (ManagerID, EmployeeID, Title, DeptID, Level) 
AS 
(
-- Anchor member definition 
    SELECT e.ManagerID, e.EmployeeID, e.Title, edh.DepartmentID, 
     0 AS Level 
    FROM dbo.MyEmployees AS e 
    INNER JOIN HumanResources.EmployeeDepartmentHistory AS edh 
     ON e.EmployeeID = edh.BusinessEntityID AND edh.EndDate IS NULL 
    WHERE ManagerID IS NULL 
    UNION ALL 
-- Recursive member definition 
    SELECT e.ManagerID, e.EmployeeID, e.Title, edh.DepartmentID, 
     Level + 1 
    FROM dbo.MyEmployees AS e 
    INNER JOIN HumanResources.EmployeeDepartmentHistory AS edh 
     ON e.EmployeeID = edh.BusinessEntityID AND edh.EndDate IS NULL 
    INNER JOIN DirectReports AS d 
     ON e.ManagerID = d.EmployeeID 
) 
-- Statement that executes the CTE 
SELECT ManagerID, EmployeeID, Title, DeptID, Level 
FROM DirectReports 
INNER JOIN HumanResources.Department AS dp 
    ON DirectReports.DeptID = dp.DepartmentID 
WHERE dp.GroupName = N'Sales and Marketing' OR Level = 0; 
GO 

Answer 3

如果我得到你的权利，你想有一个整洁的小C＃功能找到最后重定向，对不对？ 在这种情况下，这应该这样做：

string GetRedirectionFromDatabase(string requestUrl) 
{ 
    // Fetch redirect form DB, or if none exists return null 
} 

string GetFinalUrl(string requestUrl) 
{ 
    var redirection = GetRedirectionFromDatabase(requestUrl); 
    return redirection != null ? GetFinalUrl(redirection) : requestUrl; 
}